Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> c.d.o.server -> Re: Oracle Myths

Re: Oracle Myths

From: Howard J. Rogers <dba_at_hjrdba.com>
Date: Sat, 25 May 2002 08:11:55 +1000
Message-ID: <acmdu7$cdt$1@lust.ihug.co.nz>

"William Rice" <ricew_at_operamail.com> wrote in message news:1f1a539b.0205231415.51b83543_at_posting.google.com...
> "Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message
news:<3ce36ec0$0$8513$ed9e5944_at_reading.news.pipex.net>...
> <SNIP>
> > >
> > > Seperate tables and indexes for performance reasons.
> >
> > see the huge thread on this earlier at http://shrinkalink.com/201
> >
> > I think my summary of this is that in general seperating data and
indexes
> > should be done for
> > 1) management reasons only.
>
> While I didnt read the whole thread, I guess what I got from it was
> the old statement, benchmark your system and find out...
>
> <SNIP>
>
> An example of where separating indexes from a table might be
> beneficial would be if you happen to do lots of full table scans on a
> particular table. If you make it the only inhabitant of a tablespace
> (or tablespaces if it is partitioned), you avoid having to skip past
> all of the extents you are not interested in.

Myth alert. The contiguity of extents has absolutely zero bearing on performance. None whatsoever. For the simple reason that the blocks of a single extent are not physically contiguous on disk anyway. They are scattered all over the physical platter... and therefore, you are forever having to skip around the place whether there is one extent of one segment, or several thousand extents belonging to several hundred segments. It makes no difference.

Regards
HJR <I am not saying there
> are no down sides to this solution, but I think being able to fragment
> index _can_ give performance benefits in some situations.
>
> Will
> P.S. I am a bit new to the Oracle arena, but have been doing DBMS
> management for an undisclosed product for awhile :)
> P.P.S. This is assuming raw devices are used for the tablespaces
Received on Fri May 24 2002 - 17:11:55 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US